C socket TCP server fails after client disconnects - c

Question

I am modifying the server code from here http://www.linuxhowtos.org/C_C++/socket.htm. I want to reset the server when the client disconnects, so it's ready the next time for the client. But instead when I close the client side, the server shuts down and nothing is written in the server log. Since I only want to handle one client at a time, I don't need to fork right? Otherwise the server works fine and responds to messages I've sent from a client I wrote in C#.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
FILE *fp;
double square(double x)
{
return x*x;
}
void error(const char *msg)
{
fprintf(fp, "%s", msg);
fprintf(fp, "%s", "\n");
}
int main(int argc, char *argv[])
{
fp = fopen("serverlog.txt", "a");
int sockfd;
int newsockfd;
int portno = 43635;
int clientIsConnected;
socklen_t clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;
while (1)
{
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
{
error("ERROR opening socket");
close(sockfd);
return 0;
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
{
error("ERROR on binding");
close(sockfd);
return 0;
}
if (listen(sockfd,5) < 0)
{
error("ERROR on listen");
close(sockfd);
return 0;
}
clilen = sizeof(cli_addr);
newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
if (newsockfd < 0)
{
error("ERROR on accept");
close(newsockfd);
close(sockfd);
return 0;
}
clientIsConnected = 1;
while (clientIsConnected)
{
bzero(buffer, 256);
n = read(newsockfd, buffer, 255);
if (n < 0)
{
error("ERROR reading from socket");
clientIsConnected = 0;
break;
}
double x = atof(buffer);
double squared = square(x);
char response[256];
sprintf(response, "%f", squared);
n = write(newsockfd, response, strlen(response));
if (n < 0)
{
error("ERROR writing to socket");
clientIsConnected = 0;
break;
}
}
}
close(sockfd);
return 0;
}

Answer 1

It may be that your server stops because it received SIGPIPE. You can use
signal(SIGPIPE, SIG_IGN);
to keep your program going and you can handle the closed communication in your application code.